<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
<div id="app">
  <h2 :class="getClassName()">{{message}}</h2>
</div>

<script src="./js/vue.js"></script>

<script>
  const app = new Vue({
    el:'#app',
    data:{
        message:'Hello World',
        active:'active',
        line:'line'
    },
    methods:{
        getClassName:function(){
            return [this.active, this.line];
        }
    }
  });
</script>
</body>
</html>